CAMPBELL - Weebly...Concept 27.1: Structural and functional adaptations contribute to prokaryotic...

CAMPBELL

BIOLOGY Reece • Urry • Cain • Wasserman • Minorsky • Jackson

EDITION

27 Bacteria and

Archaea

Lecture Presentation by

Nicole Tunbridge and

Kathleen Fitzpatrick

Masters of Adaptation

Utah’s Great Salt Lake can reach a salt

concentration of 32%

Its pink color comes from living prokaryotes

Figure 27.1

Prokaryotes thrive almost everywhere, including

places too acidic, salty, cold, or hot for most other

organisms

Most prokaryotes are microscopic, but what they

lack in size they make up for in numbers

There are more in a handful of fertile soil than the

number of people who have ever lived

Prokaryotes are divided into two domains: bacteria

and archaea

Concept 27.1: Structural and functional adaptations contribute to prokaryotic success

Earth’s first organisms were likely prokaryotes

Most prokaryotes are unicellular, although some

species form colonies

Most prokaryotic cells are 0.5–5 µm, much smaller

than the 10–100 µm of many eukaryotic cells

Prokaryotic cells have a variety of shapes

The three most common shapes are spheres

(cocci), rods (bacilli), and spirals

Figure 27.2

(a) Spherical (b) Rod-shaped (c) Spiral 3

Figure 27.2a

(a) Spherical

Figure 27.2b

(b) Rod-shaped

Figure 27.2c

(c) Spiral

Syphilis (Treponema pallidium)

Cell-Surface Structures

An important feature of nearly all prokaryotic cells

is their cell wall, which maintains cell shape,

protects the cell, and prevents it from bursting in a

hypotonic environment

Eukaryote cell walls are made of cellulose or chitin

Bacterial cell walls contain peptidoglycan, a

network of sugar polymers cross-linked by

polypeptides

Archaea contain polysaccharides and proteins but

lack peptidoglycan

Scientists use the Gram stain to classify bacteria

by cell wall composition

Gram-positive bacteria have simpler walls with a

large amount of peptidoglycan

Gram-negative bacteria have less peptidoglycan

and an outer membrane that can be toxic

Figure 27.3

(a) Gram-positive bacteria Gram-negative

bacteria

Peptido-

glycan

Plasma

membrane

Carbohydrate portion

of lipopolysaccharide

Crystal violet is easily rinsed away, revealing

the red safranin dye.

Peptidoglycan traps crystal violet,

which masks the safranin dye.

Gram-positive

bacteria

Gram-negative

bacteria

membrane

Peptido-

glycan layer

Plasma membrane

10 µm

Figure 27.3a

(a) Gram-positive bacteria

Peptido-

glycan

Plasma

membrane

Peptidoglycan traps crystal violet,

which masks the safranin dye.

Figure 27.3b

Gram-negative

bacteria

Carbohydrate portion

of lipopolysaccharide

Crystal violet is easily rinsed away, revealing

the red safranin dye.

membrane

Peptido-

glycan layer

Plasma membrane

Figure 27.3c

Gram-positive

bacteria

Gram-negative

bacteria

10 µm

Many antibiotics target peptidoglycan and damage

bacterial cell walls

Gram-negative bacteria are more likely to be

antibiotic resistant

A polysaccharide or protein layer called a capsule

covers many prokaryotes

Figure 27.4

200 nm

Bacterial cell wall

Bacterial capsule

Tonsil cell

Many prokaryotes form metabolically inactive

endospores, which can remain viable in harsh

conditions for centuries

Figure 27.5

0.3 µm

Endospore

Some prokaryotes have fimbriae, which allow

them to stick to their substrate or other individuals

in a colony

Pili (or sex pili) are longer than fimbriae and allow

prokaryotes to exchange DNA

Figure 27.6

Fimbriae

Motility

In a heterogeneous environment, many bacteria

exhibit taxis, the ability to move toward or away

from a stimulus

Chemotaxis is the movement toward or away from

a chemical stimulus

Most motile bacteria propel themselves by flagella

scattered about the surface or concentrated at one

or both ends

Flagella of bacteria, archaea, and eukaryotes are

composed of different proteins and likely evolved

independently

Figure 27.7

20 nm Filament

Motor Cell wall

Plasma membrane Rod

Peptidoglycan layer

Flagellum

Figure 27.7a

Video: Prokaryotic Flagella

Evolutionary Origins of Bacterial Flagella

Bacterial flagella are composed of a motor, hook,

and filament

Many of the flagella’s proteins are modified

versions of proteins that perform other tasks in

bacteria

Flagella likely evolved as existing proteins were

added to an ancestral secretory system

This is an example of exaptation, where existing

structures take on new functions through descent

with modification

Internal Organization and DNA

Prokaryotic cells usually lack complex

compartmentalization

Some prokaryotes do have specialized

membranes that perform metabolic functions

These are usually infoldings of the plasma

membrane

Figure 27.8

0.2 µm 1 µm

Respiratory membrane

Thylakoid membranes

(a) Aerobic prokaryote (b) Photosynthetic prokaryote

Figure 27.8a

0.2 µm

Respiratory membrane

(a) Aerobic prokaryote

Figure 27.8b

Thylakoid membranes

(b) Photosynthetic prokaryote

The prokaryotic genome has less DNA than the

eukaryotic genome

Most of the genome consists of a circular

chromosome

The chromosome is not surrounded by a

membrane; it is located in the nucleoid region

Some species of bacteria also have smaller rings

of DNA called plasmids

Figure 27.9

Plasmids

Chromosome

There are some differences between prokaryotes

and eukaryotes in DNA replication, transcription,

and translation

These allow people to use some antibiotics to

inhibit bacterial growth without harming

themselves

Five Basic Mechanisms of Antibiotic Action against Bacterial Cells:

Inhibition of Cell Wall Synthesis (most common

mechanism)

Inhibition of Protein Synthesis (Translation)

(second largest class)

Alteration of Cell Membranes

Inhibition of Nucleic Acid Synthesis

Antimetabolite Activity

Reproduction

Prokaryotes reproduce quickly by binary fission

and can divide every 1–3 hours

Key features of prokaryotic reproduction

They are small

They reproduce by binary fission

They have short generation times

Concept 27.2: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes

Prokaryotes have considerable genetic variation

Three factors contribute to this genetic diversity

Rapid reproduction

Mutation

Genetic recombination

Rapid Reproduction and Mutation

Prokaryotes reproduce by binary fission, and

offspring cells are generally identical

Mutation rates during binary fission are low, but

because of rapid reproduction, mutations can

accumulate rapidly in a population

Their short generation time allows prokaryotes to

evolve quickly

Prokaryotes are not “primitive” but are highly

evolved

Figure 27.10

Experiment Daily serial transfer

0.1 mL (population sample)

Old tube (discarded after transfer)

New tube (9.9 mL growth medium)

Results

Experimental populations (average)

Ancestral population

tive t

ncestr

0 5,000 10,000 15,000 20,000

Generation

Genetic Recombination

Genetic recombination, the combining of DNA

from two sources, contributes to diversity

Prokaryotic DNA from different individuals can be

brought together by transformation, transduction,

and conjugation

Movement of genes among individuals from

different species is called horizontal gene transfer

Transformation and Transduction

A prokaryotic cell can take up and incorporate

foreign DNA from the surrounding environment in

a process called transformation

Transduction is the movement of genes between

bacteria by bacteriophages (viruses that infect

bacteria)

Figure 27.11-1

Phage infects bacterial donor cell with A+ and B+

alleles.

Donor cell

Phage DNA

Figure 27.11-2

alleles.

Phage DNA is replicated and proteins synthesized.

Donor cell

Phage DNA

Figure 27.11-3

alleles.

Fragment of DNA with A+ allele is packaged within a phage capsid.

Donor cell

Phage DNA

Figure 27.11-4

alleles.

Phage with A+ allele infects bacterial recipient cell.

Donor cell

Phage DNA

B− A−

Crossing over

Recipient cell

Figure 27.11-5

alleles.

Phage with A+ allele infects bacterial recipient cell.

Incorporation of phage DNA creates recombinant cell with genotype A+ B−.

Donor cell

Phage DNA

B− A−

Crossing over

Recombinant cell

Recipient cell

B− A+

Conjugation and Plasmids

Conjugation is the process where genetic

material is transferred between prokaryotic cells

In bacteria, the DNA transfer is one way

A donor cell attaches to a recipient by a pilus, pulls

it closer, and transfers DNA

A piece of DNA called the F factor is required for

the production of pili

Figure 27.12

Sex pilus

The F Factor as a Plasmid

Cells containing the F plasmid function as DNA

donors during conjugation

Cells without the F factor function as DNA

recipients during conjugation

The F factor is transferable during conjugation

Figure 27.13

Bacterial chromosome F plasmid

F+ cell

(donor)

Mating bridge

Bacterial chromosome

(a) Conjugation and transfer of an F plasmid

F− cell (recipient)

Hfr cell (donor)

F factor

Recombinand F− bacterium

(b) Conjugation and transfer of part of an Hfr bacterial chromosome, resulting in recombination

Figure 27.13a-1

F+ cell

(donor)

Mating bridge

One strand of F+ cell plasmid DNA breaks at arrowhead.

Figure 27.13a-2

F+ cell

(donor)

Mating bridge

Broken strand peels off and enters F− cell.

Figure 27.13a-3

F+ cell

(donor)

Mating bridge

Donor and recipient cells synthesize complementary DNA strands.

Figure 27.13a-4

F+ cell

(donor)

Mating bridge

Donor and recipient cells synthesize complementary DNA strands.

Recipient cell is now a recombinant F+ cell.

1 2 4 3

Figure 27.13b-1

Hfr cell (donor)

F factor

1 An Hfr cell forms a mating bridge with an F− cell.

Figure 27.13b-2

Hfr cell (donor)

F factor

1 2 An Hfr cell forms a mating bridge with an F− cell.

A single strand of the F factor breaks and begins to move through the bridge.

Figure 27.13b-3

Hfr cell (donor)

F factor

1 2 3 An Hfr cell forms a mating bridge with an F− cell.

Crossing over can result in exchange of homologous genes.

Figure 27.13b-4

Hfr cell (donor)

F factor

Recombinand F− bacterium

1 2 4 3 An Hfr cell forms a mating bridge with an F− cell.

Crossing over can result in exchange of homologous genes.

Enzymes degrade and DNA not incorporated. Recipient cell is now a recombinant F− cell.

The F Factor in the Chromosome

A cell with the F factor built into its chromosomes

functions as a donor during conjugation

The recipient becomes a recombinant bacterium,

with DNA from two different cells

R Plasmids and Antibiotic Resistance

R plasmids carry genes for antibiotic resistance

Antibiotics kill sensitive bacteria, but not bacteria

with specific R plasmids

Through natural selection, the fraction of bacteria

with genes for resistance increases in a population

exposed to antibiotics

Antibiotic-resistant strains of bacteria are

becoming more common

Concept 27.3: Diverse nutritional and metabolic adaptations have evolved in prokaryotes

Prokaryotes can be categorized by how they

obtain energy and carbon

Phototrophs obtain energy from light

Chemotrophs obtain energy from chemicals

Autotrophs require CO2 as a carbon source

Heterotrophs require an organic nutrient to make

organic compounds

Energy and carbon sources are combined to give

four major modes of nutrition

Photoautotrophy

Chemoautotrophy

Photoheterotrophy

Chemoheterotrophy

Table 27.1

The Role of Oxygen in Metabolism

Prokaryotic metabolism varies with respect to O2

Obligate aerobes require O2 for cellular respiration

Obligate anaerobes are poisoned by O2 and use

fermentation or anaerobic respiration

Facultative anaerobes can survive with or

without O2

Nitrogen Metabolism

Nitrogen is essential for the production of amino

acids and nucleic acids

Prokaryotes can metabolize nitrogen in a variety of

In nitrogen fixation, some prokaryotes convert

atmospheric nitrogen (N2) to ammonia (NH3)

Metabolic Cooperation

Cooperation between prokaryotes allows them to

use environmental resources they could not use

as individual cells

In the cyanobacterium Anabaena, photosynthetic

cells and nitrogen-fixing cells called heterocysts

(or heterocytes) exchange metabolic products

Figure 27.14

Photosynthetic cells

Heterocyst

20 µm

Metabolic cooperation occurs between different

prokaryotic species in surface-coating colonies

called biofilms

Sulfate-consuming bacteria and methane-

consuming bacteria on the ocean floor use each

other’s waste products

Concept 27.4: Prokaryotes have radiated into a diverse set of lineages

Prokaryotes inhabit every environment known to

support life

Advance in genomics are beginning to reveal the

extent of prokaryotic diversity

An Overview of Prokaryotic Diversity

Genetic analysis lead to the division of

prokaryotes into two domains, Bacteria and

Archaea

Molecular systematists continue to work on the

phylogeny of prokaryotes

Figure 27.15

UNIVERSAL ANCESTOR

Eukaryotes

Korarchaeotes

Euryarchaeotes

Crenarchaeotes

Nanoarchaeotes

Proteobacteria

Chlamydias

Spirochetes

Cyanobacteria

Gram-positive bacteria

The use of polymerase chain reaction (PCR) has

allowed for more rapid sequencing of prokaryote

genomes

A handful of soil may contain 10,000 prokaryotic

species

Horizontal gene transfer between prokaryotes

obscures the root of the tree of life

Bacteria

Bacteria include the vast majority of prokaryotic

species familiar to most people

Diverse nutritional types are represented among

bacteria

Figure 27.UN01

Eukarya

Archaea

Bacteria

Proteobacteria

These gram-negative bacteria include

photoautotrophs, chemoautotrophs, and

heterotrophs

Some are anaerobic, and others aerobic

Figure 27.16aa

Epsilon

Proteobacteria

Subgroup: Alpha Proteobacteria

Many species are closely associated with

eukaryotic hosts

Scientists hypothesize that mitochondria evolved

from aerobic alpha proteobacteria through

endosymbiosis

Figure 27.16ab

Alpha subgroup

Rhizobium (arrows) inside a root cell of a legume (TEM)

Example: Rhizobium, which forms root nodules in

legumes and fixes atmospheric N2

Example: Agrobacterium, which produces tumors

in plants and is used in genetic engineering

Subgroup: Beta Proteobacteria

Example: the soil bacterium Nitrosomonas, which

converts NH4+ to NO2

Figure 27.16ac

Beta subgroup

Nitrosomonas (colorized TEM)

Subgroup: Gamma Proteobacteria

Examples include sulfur bacteria such as

Thiomargarita namibiensis and pathogens such as

Legionella, Salmonella, and Vibrio cholerae

Escherichia coli resides in the intestines of many

mammals and is not normally pathogenic

Figure 27.16ad

Gamma subgroup

200 µ

Thiomargarita namibiensis containing sulfur wastes (LM)

Subgroup: Delta Proteobacteria

Example: the slime-secreting myxobacteria, which

produces drought resistant “myxospores”

Example: bdellovibrios, which mount high-speed

attacks on other bacteria

Figure 27.16ae

Delta subgroup

Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM)

300 µ

Subgroup: Epsilon Proteobacteria

This group contains many pathogens including

Campylobacter, which causes blood poisoning,

and Helicobacter pylori, which causes stomach

ulcers

Figure 27.16af

Helicobacter pylori (colorized TEM)

Epsilon subgroup

Chlamydias

These bacteria are parasites that live within animal

Chlamydia trachomatis causes blindness and

nongonococcal urethritis by sexual transmission

Figure 27.16ba

Chlamydias

Chlamydia (arrows) inside an animal cell (colorized TEM)

Spirochetes

These bacteria are helical heterotrophs

Some are parasites, including Treponema

pallidum, which causes syphilis, and Borrelia

burgdorferi, which causes Lyme disease

Figure 27.16bb

Spirochetes

Leptospira, a spirochete (colorized TEM)

Cyanobacteria

These are photoautotrophs that generate O2

Plant chloroplasts likely evolved from

cyanobacteria by the process of endosymbiosis

Figure 27.16bc

Cyanobacteria

Oscillatoria, a filamentous cyanobacterium

Video: Cyanobacteria (Oscillatoria)

Gram-Positive Bacteria

Gram-positive bacteria include

Actinomycetes, which decompose soil

Bacillus anthracis, the cause of anthrax

Clostridium botulinum, the cause of botulism

Some Staphylococcus and Streptococcus, which

can be pathogenic

Mycoplasms, the smallest known cells

Figure 27.16bd

Streptomyces, the source of many antibiotics (SEM)

Figure 27.16be

Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM)

Archaea

Archaea share certain traits with bacteria and

other traits with eukaryotes

Figure 27.UN02

Eukarya

Archaea

Bacteria

Table 27.2

Table 27.2a

Table 27.2b

Some archaea live in extreme environments and

are called extremophiles

Extreme halophiles live in highly saline

environments

Extreme thermophiles thrive in very hot

environments

Figure 27.17

Video: Tube Worms

Methanogens live in swamps and marshes and

produce methane as a waste product

Methanogens are strict anaerobes and are

poisoned by O2

In recent years, genetic prospecting has revealed

many new groups of archaea

Some of these may offer clues to the early

evolution of life on Earth

Concept 27.5: Prokaryotes play crucial roles in the biosphere

Prokaryotes are so important that if they were to

disappear the prospects for any other life surviving

would be dim

Chemical Recycling

Prokaryotes play a major role in the recycling of

chemical elements between the living and

nonliving components of ecosystems

Chemoheterotrophic prokaryotes function as

decomposers, breaking down dead organisms

and waste products

Prokaryotes can sometimes increase the

availability of nitrogen, phosphorus, and potassium

for plant growth

Figure 27.18

No bacteria

Strain 1 Strain 2 Strain 3

Soil treatment

Seedlings growing in the lab U

Figure 27.18a

Seedlings growing in the lab

Prokaryotes can also “immobilize” or decrease the

availability of nutrients

Ecological Interactions

Symbiosis is an ecological relationship in which

two species live in close contact: a larger host and

smaller symbiont

Prokaryotes often form symbiotic relationships

with larger organisms

In mutualism, both symbiotic organisms benefit

In commensalism, one organism benefits while

neither harming nor helping the other in any

significant way

In parasitism, an organism called a parasite

harms but does not kill its host

Parasites that cause disease are called

pathogens

Figure 27.19

The ecological communities of hydrothermal vents

depend on chemoautotrophic bacteria for energy

Concept 27.6: Prokaryotes have both beneficial and harmful impacts on humans

Some prokaryotes are human pathogens, but

others have positive interactions with humans

Mutualistic Bacteria

Human intestines are home to about 500–1,000

species of bacteria

Many of these are mutualists and break down food

that is undigested by our intestines

Pathogenic Bacteria

Bacteria cause about half of all human diseases

Some bacterial diseases are transmitted by other

species

For example, Lyme disease is caused by a

bacterium and carried by ticks

Figure 27.20

Figure 27.20a

Figure 27.20b

Figure 27.20c

Pathogenic prokaryotes typically cause disease by

releasing exotoxins or endotoxins

Exotoxins are secreted and cause disease even if

the prokaryotes that produce them are not present

Endotoxins are released only when bacteria die

and their cell walls break down

Horizontal gene transfer can spread genes

associated with virulence

For example, pathogenic strains of E. coli contain

genes that were acquired through transduction

Prokaryotes in Research and Technology

Experiments using prokaryotes have led to

important advances in DNA technology

For example, E. coli is used in gene cloning

For example, Agrobacterium tumefaciens is used to

produce transgenic plants

Bacteria can now be used to make natural plastics

Figure 27.21

Prokaryotes are the principal agents in

bioremediation, the use of organisms to remove

pollutants from the environment

Bacteria can be engineered to produce vitamins,

antibiotics, and hormones

Figure 27.22

Bacteria are also being engineered to produce

ethanol from agricultural and municipal waste

biomass, switchgrass, and corn

Figure 27.23

Figure 27.16a

Epsilon

Proteo- bacteria

Alpha subgroup Beta subgroup

Rhizobium (arrows) (TEM)

Nitrosomonas (TEM)

Gamma subgroup

Delta subgroup

Thiomargarita namibiensis (LM)

Chondromyces crocatus (SEM)

Helicobacter pylori (TEM)

Epsilon subgroup

Figure 27.16b

Chlamydias

Chlamydia (arrows) (TEM)

Spirochetes

Leptospira (TEM)

Cyanobacteria

Oscillatoria

Streptomyces (SEM)

Mycoplasmas (SEM)

Figure 27.UN03a

Soil Treatment Average Percentage of

Seedlings Afflicted with Fungal Disease

Disease-suppressive soil

Soil from margin of field

Soil from margin of field + 10% disease-suppressive soil

Disease-suppressive soil heated to 50℃ for 1 hour

Disease-suppressive soil heated to 80℃ for 1 hour

Figure 27.UN03b

Figure 27.UN04

Fimbriae

Cell wall

Capsule

Internal organization

Flagella

Circular chromosome

Sex pilus

Figure 27.UN05

Rhizobium strain

Plant mass (g)

Source: J. J. Burdon et al., Variation in the effectiveness of symbiotic asso- ciations between native rhizobia and temperate Australian Acacia: within species interactions, Journal of Applied Ecology 36:398–408 (1999).

Note: Without Rhizobium, after 12 weeks, Acacia plants have a mass of about 0.1 g.

1 2 3 4 5 6

0.91 0.06 1.56 1.72 0.14 1.03

Figure 27.UN06

CAMPBELL - Weebly...Concept 27.1: Structural and functional adaptations contribute to prokaryotic...

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